my labour sounds very much like yours, minus the back pain, all of a sudden i was having contractions, they were hard and fast, no build up to get me ready i pretty much got thrown in the deep end
After a couple of hours i was telling them she was ready to come but they didnt believe me coz this was my first, but they checked me out and i was fully dialated and ready to push.
As far as how i coped, at first i didnt cope very well, i wasnt prepared for it to be so full on right away, they gave me gas but for an hour and a half of my sucking on it it wasnt even switched on as soon as i got the gas, i seemed to full into a "zone" and i think i coped pretty well, it was almost like i was outside myself watching me (if that makes sense)
My next baby i will be much mpre prepared, i know it might not go the same way, but i know what im in for this time lol.